Use symlink source when inspecting current permissions

Fixes CHEF-4341 http://tickets.opscode.com/browse/CHEF-4341

When manage_symlink_source is enabled, File providers update
current_resource with the security attributes of the source file.
Subsequent actions (e.g., running FileAccessControl) use the values set
on current_resource to determine if they need to modify the system, so
setting them incorrect leads to a file resource being (not) updated
incorrectly.